Reducing the Amount of Waste Activated Sludge

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Reducing the Amount of Waste Activated Sludge

• Sara Schmidt
• CE 479
• December 6, 2006

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Overview of Presentation

• Background information
• Concerns regarding waste activated sludge
• What is MicroSludge?
• Design comparisons of two digester systems

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Background Information

• Primary sludge produced from the primary
  settling of untreated wastewater
• Waste activated sludge (WAS) excess sludge
  produced from activated sludge process
• CMAD Conventional Mesophilic Anaerobic Digester
• Mesophilic operating temperature of 25 - 40C

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Background Information

• Thermophilic operating temperature of 50-60C
• MicroSludge Sludge pre-treatment that greatly
  enhances the performance of digesters

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Concerns Regarding WAS

• Risks to public health from sludge residuals
• High capital and operating costs
• Contribute to the publics growing concerns
  regarding odors
• Negative environmental impacts

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How much waste do people really produce?

• A typical secondary wastewater treatment plant
  that serves 1 million people generates 25
  football fields (about three feet deep) of
  biosolids each year.

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What is MicroSludge?

• MicroSludge works by destroying microbial cell
  membranes and enabling anaerobic digesters to
  achieve significantly greater conversion of WAS
  to biogas.

www.microsludge.com
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MicroSludge and Microbes

• The image to the left shows intact microbes
  (magnified 20,000 times)
• The image to the right shows the same microbes
  after the MicroSludge process

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Benefits of MicroSludge

• Major reduction in WAS residual biosolids (VSr)
• Lowers retention time gt additional digester
  capacity
• Increased amount of biogas production
• Reduces operating, disposal, mixing costs

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MicroSludge Location in a Wastewater Treatment
Plant
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Design Parameters (Design 1)

• Q 2Mgal/d 7440 m3/d
• Dry volatile solids 0.16 kg/m3
• Biodegradable COD removed 0.17 kg/m3
• HRT (hydraulic retention time) 15 days
• Efficiency of waste utilization, E overall VSr
  Mass fractionPS x VSrPS Mass fractionTWAS x
  VSrTWAS (0.65 x 0.68) (0.35 x 0.45) 0.60 E

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Design Parameters

• Y 0.08kg VSS/kg bCOD utilized
• Kd 0.03d-1
• Digester gas is 65 methane
• Sludge contains 94 moisture, 6 solids 0.06
  Ps
• Sludge has a specific gravity, Ssl 1.02

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Calculations

• Sludge volume
• Ms (Ssl)(?w)(Ps)
• (0.16 kg/m3)(7440 m3/d)
• 1.02(103 kg/m3)(0.06)
• 19.45 m3/d

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Calculations

• bCOD loading
• (0.17 kg/m3)(7440 m3/d)
• 1265 kg/d
• HRT V/Q gt V Q HRT
• (19.45 m3/d)(15 d)
• V1 292 m3

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Calculations

• bCOD in inffluent, So
• So 1265 kg/d
• bCOD in effluent, S
• S 1265(1 - E)
• 1265(1 0.60) 506 kg/d

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Calculations

• Quantity of volatile solids produced per day, Px
• Px Y(So S) 1 (kd)(HRT)
• 0.08kg VSS/kg bCOD(759)
• 1 (0.03d-1)(15 d)
• Px(1) 41.88 kg/d

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Calculations

• Volume of methane produced per day _at_ 35C, VCH4
• VCH4 (0.40)(So S) 1.42Px
• (0.40m3/kg)759 kg/d
• 1.42(41.88 kg/d)
• VCH4 280 m3/d
• Estimate total gas production
• 280/0.65 430 m3/d

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Design Parameters (Design 2)

• Q 2Mgal/d 7440 m3/d
• Dry volatile solids 0.16 kg/m3
• Biodegradable COD removed 0.17 kg/m3
• HRT (hydraulic retention time) 15 days
• Efficiency of waste utilization, E overall VSr
  Mass fractionPS x VSrPS Mass fractionTWAS x
  VSrTWAS (0.65 x 0.68) (0.35 x 0.97) 0.78 E

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Design Parameters

• Y 0.08kg VSS/kg bCOD utilized
• Kd 0.03d-1
• Digester gas is 65 methane
• Sludge contains 94 moisture, 6 solids 0.06
  Ps
• Sludge has a specific gravity, Ssl 1.02

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Calculations

• Sludge volume
• Ms (Ssl)(?w)(Ps)
• (0.16 kg/m3)(7440 m3/d)
• 1.02(103 kg/m3)(0.06)
• 19.45 m3/d

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Calculations

• bCOD loading
• (0.17 kg/m3)(7440 m3/d)
• 1265 kg/d
• HRT V/Q gt V Q HRT
• (19.45 m3/d)(13 d)
• V2 253 m3

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Calculations

• bCOD in inffluent, So
• So 1265 kg/d
• bCOD in effluent, S
• S 1265(1 - E)
• 1265(1 0.78) 278 kg/d

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Calculations

• Quantity of volatile solids produced per day, Px
• Px Y(So S) 1 (kd)(HRT)
• 0.08kg VSS/kg bCOD(987)
• 1 (0.03d-1)(13 d)
• Px(2) 56.79 kg/d

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Calculations

• Volume of methane produced per day _at_ 35C, VCH4
• VCH4 (0.40)(So S) 1.42Px
• (0.40m3/kg)987 kg/d
• 1.42(56.79 kg/d)
• VCH4 362 m3/d
• Estimate total gas production
• 362/0.65 557 m3/d

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Comparison of two designs

• Without using MicroSludge (Design 1)
• V(1) 292 m3
• Px(1) 41.88 kg/d
• VCH4 280 m3/d
• With using MicroSludge (Design 2)
• V(2) 253 m3
• Px(2) 56.79 kg/d
• VCH4 362 m3/d

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Cost Comparison

• The major difference between these two designs
  are the volume needed for the digesters, volatile
  solids production, and methane gas production .
• These differences are a major cost reductions for
  a wastewater treatment plant.

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• Questions???